HOPS and Vps13 Have Antagonistic Roles in Regulating Lipid Droplet Morphology.

Lipid droplets are dynamic organelles that store neutral lipids (mostly triacylglycerols and sterol esters) and are bound by a single phospholipid monolayer. The formation and breakdown of the droplets are important for cellular metabolism; however, the molecular mechanisms regulating their biogenesis and turnover are still obscure. In this study, we used Erg6-yeGFP as a lipid droplet marker, isolated 1100 temperature-sensitive mutants, and observed lipid droplet morphology in these mutants by fluorescence microscopy. Six mutants with abnormal lipid droplet morphology were obtained and next-generation sequencing identified responsible mutations in genes encoding subunits of HOPS complex or its binding partner Ypt7. Therefore, the genetic screen indicated that the HOPS complex plays a critical role in maintaining lipid droplet morphology. In the absence of Vps11, vacuoles were fragmented with dot-like structures and degradation of lipid droplet surface protein Erg6 (under glucose starvation condition) decreased dramatically. A genetic screen for mutations that could rescue the abnormal lipid droplet morphology in